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Bolt Failure-Alt to Engine Bracket
I’ve now had 3 bolts shear off under vibration (2 were grade 8, 1 was an emergency grade 5) from the alternator mounting bracket where it bolts to the S60. The bottom bolt which appears to thread into the engine is fine, but the middle and upper through bolts with nuts behind are failing. Any help?
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13 Replies
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I think there should be a support brace that attaches under the alternator and then extendes down to the block. Are those bolts OK?
Ken
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Joel,
Is it the 3 that bolt the support cradle to the engine? It may be misaligned a little and when the bolts are tightened down, they eventually fail. Probably have to remove the alternator (ouch) and then align the mount to the engine and see if there are any gaps that may need to be shimmed to bolt up smooth. Just a guess.
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I think the problem lies with the bolt that is in stress, not the three that are subject to shear.
Look carefully at the coach (and Tom’s photo) and in the top of the casting towards the rear of the engine you will see a bolt under tension going into the engine block. It is hard to see and easy to miss. That bolt is oriented 90 degrees from the other three.
If that has failed or is loose the casting will try to rotate around one of the three through bolts and subject the other two to shear forces.
Let us know.
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Upon a much closer look at Tom’s photo what I thought was the 4th bolt is actually not seen in the photo. I was seeing a hose in the background. But there has to be that 4th bolt and that is key to keeping the shear forces from the three bolts shown in the photo.
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I’m not aware of a lower support bracket, but it could be missing or I could have missed it. Sounds like addl support would be the solution. I’ll take another look.
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I’ve removed the alternator bracket from a couple of 12.7s and like Jon said there were some spacers in that area. Also the ones I disassembled had that extra support brace in the rear. Not sure if they all do. If Tom’s has it maybe he can get a picture.
Ken
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The alternators I have removed from the 60 series have a support bracket and never use a regular grade 8 bolt use only a good grade of flange bolts
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This is where the 4th bolt is on mine. Difficult to see. It is where my arrow points (top center)
My crude arrow is black and hard to see, like the bolt.
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This is the brace I was thinking of.
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How do the bolts fail? Fatigue cracks, fretting, or?
If you are using off the shelf bolts, make sure that the threaded portion does not extend into the portion that is in shear. Otherwise the bolt will invariably fail due to stress risers/fatigue. It might be worthwhile to get the correct bolts from Detroit and torque them according to service manual specs.
If you keep eating bolts, you should take a hard look at your belt tensioner. On trucks they seem to get replaced regularly.
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I’ve been told that is the new S60 engine PC is giving away at the Branson rally for a grand prize😳😳😳😳
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Hey Buddy, I haven’t seen that donation you sent for the engine purchase?:)
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CHECKS IN THE MAIL.
That was my last check to so if the post office, (you know how they are) lost it, I’ll have to do it next year.
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